将一个回调作为upload_to传递给FileField [英] passing a callback as upload_to to FileField

问题描述

我有一个抽象的模型类UploadItem来处理上传的文件。我希望每个子类能够定义upload_to路径。为此，我将一个回调传递给FileField的构造函数。

这是一个例子：

  class UploadItem（models.Model）：
 file = models.FileField（upload_to = UploadItem.get_directory）
 
 
 class Meta：
 abstract = True 
＃我想让视频存储在'videos /'目录中
 class视频（UploadItem）：
 def get_directory（self，instance，filename）：
 return'视频/'
  

但是这不行，我得到这个错误：

  file = models.FileField（upload_to = UploadItem.get_directory）
 NameError：name'UploadItem'未定义
  




解决方案

错误是自然的，因为在评估

$ b时
$ b

  file = models.FileField（upload_to = UploadItem.get_directory）
  

尚未定义 UploadItem 类。您可以执行以下操作使其正常工作：

  def get_directory（）：
 pass 
 
 class UploadItem（models.Model）：
 file = models.FileField（upload_to = get_directory）
 
 class Meta：
 abstract = True 
  

这不会解决你所有的问题。在视频类中添加（或覆盖）方法 get_directory 不会更改 upload_to 属性的文件属性。

更新

文档说， upload_to 可以是可调用的。

这也可以是一个可调用的函数，例如函数，将被调用来获取上传路径，包括文件名。此可调用必须能够接受两个参数，并返回一个Unix样式的路径（带有斜杠），以传递到存储系统。

鉴于此，我们可以编写一个自定义回调函数，如下所示：

  categories_and_paths = {'video'：'videos /'，'photo'：'照片/'}＃等
 def get_directory（instance，filename）：
 category = instance.category 
 return categories_and_paths.get（category，''）
  

Instance 这里将是相应模型的实例。为此，每个模型实例应该有一个类别字段。我们可以在模型的正文中添加一个。

  class Video（UploadItem）：
 category ='video' 
  

I have an abstract model class UploadItem for handling uploaded files. I want each subclass to be able to define the upload_to path. For this, i pass a callback to the constructor of FileField.

This is an example:

class UploadItem(models.Model):
    file = models.FileField(upload_to=UploadItem.get_directory) 


    class Meta:
        abstract = True
# I want videos to be storred in 'videos/' directory
class Video(UploadItem):
    def get_directory(self, instance, filename):
        return 'videos/'

But this doesn't work, i am getting this error:

file = models.FileField(upload_to=UploadItem.get_directory) 
NameError: name 'UploadItem' is not defined

解决方案

The error is natural given that at the time of evaluating

file = models.FileField(upload_to=UploadItem.get_directory) 

the UploadItem class is not yet defined. You can do the following to make it work:

def get_directory():
    pass

class UploadItem(models.Model):
    file = models.FileField(upload_to=get_directory)

    class Meta:
        abstract = True

This won't solve all your problems though. Adding (or overriding) a method get_directory in the Video class will not change the upload_to property of the file attribute of the model.

Update

The documentation says that the upload_to can be a callable.

This may also be a callable, such as a function, which will be called to obtain the upload path, including the filename. This callable must be able to accept two arguments, and return a Unix-style path (with forward slashes) to be passed along to the storage system.

Given this we can write a custom call back function like this:

categories_and_paths = { 'video': 'videos/', 'photo': 'photos/' } # etc.
def get_directory(instance, filename):
    category = instance.category
    return categories_and_paths.get(category, '')

Instance here will be the instance of the respective model. For this to work each model instance should have a category field. We can add one in the body of the model.

class Video(UploadItem):
    category = 'video'

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